Hollow filament nylon yarns which have one or more continuous axially extending voids running through the filaments are known in the art. The shape of the filament cross-section, number and location of voids, size and shape of voids all affect the filaments' bulk, soil hiding ability and luster.
The size (cross-sectional area) of the voids decreases considerably during the spinning process from the time that the filaments emerge from the spinneret until they are fully quenched. The size of the decrease may be minimized by increasing the melt viscosity of the polyamide or by cooling the filaments more rapidly as they emerge from the spinneret. East German Economic Patent 583 34 discloses the use of 0.02 to 3% of a neutral tenside additive (e.g. ethoxylated or oxypropylated alcohols, fatty acid esters and long-chain fatty amines) which when added to the molten polyamide prior to spinning minimizes the decrease in void size.
The use of very high viscosity polyamides can lead to spinning problems due to the propensity of such polyamides to cross-link. Molten filaments are generally cooled by blowing a cool gas over them as they emerge from the spinneret. Increasing the flowrate of cool gas so as to cool the filaments more rapidly causes the filaments to become unstable in the quench chimney which in turn causes processing problems. Introducing additives such as ethoxylated or oxypropylated compounds which are incompatible with the fiber-forming polyamide may adversely affect the luster, strength and processability of the filaments.